1. Field of the Invention
The present invention relates to a low-noise block down-converter (hereinafter referred to as an LNB) and a satellite broadcasting receiving apparatus, and specifically, to an LNB and a satellite broadcasting receiving apparatus suitable for receiving a plurality of types of polarization signals transmitted from each of a plurality of satellites.
2. Description of the Background Art
Conventionally, an LNB for receiving two polarization signals transmitted from a satellite and converting the polarization signals into intermediate frequencies has been developed.
For example, Japanese Patent Laying-Open No. 5-315989 discloses an LNB that receives two polarization signals and converts the frequency of one polarization signal into a normal frequency, and converts the frequency of the other polarization signal into a frequency shifted by a certain amount from the normal frequency. Then, the LNB performs frequency-multiplexing of these frequency-converted signals to be output as one signal.
Thus, two polarization signals transmitted from one satellite can be output to a tuner through one cable.
Currently, at west longitude 101°, 110° and 119° in the sky of the United States, digital broadcasting satellites (DBSs) are launched. EchoStar (EchoStar is a trademark of EchoStar Communications Corporation, USA), one of service providers of DBS broadcastings in the United States, has obtained broadcasting rights of the satellites at west longitude 110° and 119°, and has been providing satellite broadcastings. Therefore, an LNB that receives polarization signals from such two satellites and converts these polarization signals into intermediate frequencies is required.
FIG. 9 shows a configuration of an LNB in which the LNB disclosed in Japanese Patent Laying-Open No. 5-315989 is expanded to be capable of receiving polarization signals transmitted from two satellites. Referring to FIG. 9, LNB 500 includes low-noise amplifiers 3A, 3B, 4A, and 4B, image-remove filtering circuits 5A, 5B, 6A, and 6B, local oscillators 13 and 14, frequency converting circuit 30A and 30B, signal couplers 11A and 11B, a 2×2 switching circuit 15, a microcomputer 46, intermediate frequency amplifiers 17A and 17B, capacitors 18A and 18B, output terminals 20A and 20B, and power source circuit 22.
To LNB 500, a left-hand polarization signal transmitted from the satellite at west longitude 119° (hereinafter referred to as “119° left-hand polarization signal” and “119° satellite”, respectively), a right-hand polarization signal transmitted from 119° satellite (hereinafter referred to as “119° right-hand polarization signal”), a left-hand polarization signal transmitted from the satellite at west longitude 110° (hereinafter referred to as “110° left-hand polarization signal” and “110° satellite”, respectively), and a right-hand polarization signal transmitted from 110° satellite (hereinafter referred to as “110° right-hand polarization signal”) are input. The frequencies of these input signals are included in the 0th frequency band (12.2 GHz–12.7 GHz).
Low-noise amplifier 3A receives 119° left-hand polarization signal and performs low-noise amplification thereof. Low-noise amplifier 4A receives 119° right-hand polarization signal and performs low-noise amplification thereof. Low-noise amplifier 4B receives 110° right-hand polarization signal and performs low-noise amplification thereof. Low-noise amplifier 3B receives 110° left-hand polarization signal and performs low-noise amplification thereof.
Image-remove filtering circuits 5A, 6A, 6B, and 5B remove image signals from low-noise amplified 119° left-hand polarization signal, low-noise amplified 119° right-hand polarization signal, low-noise amplified 110° right-hand polarization signal, and low-noise amplified 110° left-hand polarization signal, respectively.
Local oscillators 13 and 14 generate sine-wave signals (local oscillator signals) of 11.25 GHz, 14.35 GHz, respectively.
Frequency converting circuit 30A corresponds to 119° satellite, and includes mixers 7A and 8A, a high pass filter 9A and a low pass filter 10A, and converts the frequency bands of 119° left-hand polarization signal and 119° right-hand polarization signal into two intermediate frequency (IF) bands that do not overlap with each other.
Mixer 7A mixes 119° left-hand polarization signal, of which frequency is included in the 0th frequency band (12.2–12.7 GHz) and which has been low-noise amplified and removed of image signals, and a local oscillator signal of 14.35 GHz, to output 119° left-hand polarization signal of which frequency is included in a first IF frequency band (frequency 1650 MHz–2150 MHz, hereinafter also referred to as “high band”).
Mixer 8A mixes 119° right-hand polarization signal, of which frequency is included in the 0th frequency band (12.2–12.7 GHz) and which has been low-noise amplified and removed of image signals, and a local oscillator signal of 11.25 GHz, to output 119° right-hand polarization signal of which frequency is included in a second IF frequency band (frequency 950 MHz–1450 MHz, hereinafter also referred to as “low band”).
High pass filter 9A passes 119° left-hand polarization signal, of which frequency is included in the first IF frequency band, and which is output from mixer 7A.
Low pass filter 10A passes 119° right-hand polarization signal, of which frequency is included in the second IF frequency band, and which is output from mixer 8A.
Frequency converting circuit 30B corresponds to 110° satellite, and includes mixers 7B and 8B, a high pass filter 9B and a low pass filter 10B, and converts the frequency bands of 110° left-hand polarization signal and 110° right-hand polarization signal into two intermediate frequency (IF) bands that do not overlap with each other.
Mixer 8B mixes 110° right-hand polarization signal, of which frequency is included in the 0th frequency band (12.2–12.7 GHz) and which has been low-noise amplified and removed of image signals, and a local oscillator signal of 11.25 GHz, to output 110° right-hand polarization signal of which frequency is included in the second IF frequency band.
Mixer 7B mixes 110° left-hand polarization signal, of which frequency is included in the 0th frequency band (12.2–12.7 GHz) and which has been low-noise amplified and removed of image signals, and a local oscillator signal of 14.35 GHz, to output 110° left-hand polarization signal of which frequency is included in a first IF frequency band.
High pass filter 9B passes 110° left-hand polarization signal of which frequency is included in the first IF frequency band, and which is output from mixer 7B.
Low pass filter 10B passes 110° right-hand polarization signal of which frequency is included in the second IF frequency band, and which is output from mixer 8B.
Signal coupler 11A corresponds to 119° satellite, and performs frequency-multiplexing of 119° left-hand polarization signal that has passed high pass filter 9A and 119° right-hand polarization signal that has passed low pass filter 10A, to output a combined 119° signal. Accordingly, combined 119° signal is a signal in which 119° left-hand polarization signal is arranged on high-band side, and 119° right-hand polarization signal is arranged on low-band side.
Signal coupler 11B corresponds to 110° satellite, and performs frequency-multiplexing of 110° right-hand polarization signal that has passed low pass filter 10B and 110° left-hand polarization signal that has passed high pass filter 9B, to output a combined 110° signal. Accordingly, combined 110° signal is a signal in which 110° left-hand polarization signal is arranged on high-band side, and 110° right-hand polarization signal is arranged on low-band side.
2×2 switching circuit 15 operates at IF frequency band (frequency 950 MHz∫2150 MHz). 2×2 switching circuit 15 receives combined 119° signal and combined 110° signal at terminals I1 and I2, respectively. 2×2 switching circuit 15 follows the instruction of microcomputer 46 and outputs combined 119° signal or combined 110° signal to each of terminals O1 and O2.
Intermediate frequency amplifiers 17A and 17B amplify output signals of terminals O1 and O2, respectively.
Capacitors 18A and 18B remove low-frequency noise of output signals of intermediate frequency amplifiers 17A and 17B, respectively.
Power source circuit 22 supplies power to components of LNB 500.
Output terminal 20A outputs an output signal of terminal O1 that has been amplified and removed of low-frequency noise (i.e., combined 119° signal or combined 110° signal) to tuner 1. Output terminal 20B outputs an output signal of terminal O2 that has been amplified and removed of low-frequency noise (i.e., combined 119° signal or combined 110° signal) to tuner 2.
FIG. 10 shows combinations of signals that can be output simultaneously through one cable by LNB 500. As shown in FIG. 10, combinations of signals that can be output are two, since LNB 500 outputs combined 110° signal (110° right-hand polarization signal on low-band side and 110° left-hand polarization signal on high-band side), or combined 119° signal (119° right-hand polarization signal on low-band side and 119° left-hand polarization signal on high-band side).
As described above, by LNB 500, combined 119° signal in which 119° right-hand polarization signal and 119° left-hand polarization signal are combined, or combined 110° signal in which 110° right-hand polarization signal and 110° left-hand polarization signal are combined can be output to tuners 1 and 2.
However, with LNB 500 as described above, what is simultaneously transmitted to a tuner through one cable are 119° right-hand polarization signal and 119° left-hand polarization signal, or 110° right-hand polarization signal an 110° left-hand polarization signal.
Specifically, with one cable, polarization signals of either 119° satellite or 110° satellite only can be transmitted simultaneously, and polarization signals from two satellites, such as 119° right-hand polarization signal and 110° left-hand polarization signal can not be output simultaneously.